In a TDMA communication system a plurality of subscriber units (e.g., portable two-way radios) share a number of time slots that are assigned by a system controller based on availability. The subscriber units communicate with each other and with other communication units via a plurality of base stations. In such communication systems, some mechanism must be provided to allow subscribers operating within the system to roam or travel about the area served by the communication system. For example, conventional cellular telephone systems divide a geographic area into several "cells", each of which contains one or more multi-channel base stations controlled by a cell site controller. Each cell site controller determines the received signal strength of each call in progress, and forwards this information to a network controller. The network controller uses the signal strength information to determine when one cell should "hand-off" a call to another cell. In this way, communication is maintained as subscribers roam from cell to cell. In TDMA systems, different processes are required for channel (i.e., time slot) acquisition by subscriber units and handoff.